A capillary is one of the tube-shaped blood vessels that carry blood away from the arterioles to the body's tissues and organs. When a capillary is impaired, radiofrequency (RF) therapy can be applied to the capillary to treat the tissue. To ensure appropriate treatment, temperature at the lesion is sensed and the temperature reading is transmitted to an external monitor for temperature monitoring and for controlling RF energy delivery. It is also important that the force at the catheter tip is within reasonably acceptable range so that not to injure the tissue. A typical ablation device includes an electrode for RF energy delivery and a temperature sensor for measuring tissue temperature. The bulky size of said ablation device comprising an electrode and a temperature probe might pose safety concerns to a patient when it is forced into a restricted place. A miniature RF-delivery apparatus is needed to pass into tiny openings for capillary treatment, the apparatus preferably having temperature sensing means for sensing/controlling the RF energy delivery and force measuring means for sensing/controlling apparatus advancement.
A liver cancer or tumor is difficult to treat because of its softness. RF therapy has been applied to treat the liver tissue. It is also important that the force at the catheter tip is within reasonably acceptable range for contacting the liver tissue so that not to injure the liver tissues. However, the existing ablation device can only treat the surface of the liver because of its bulky construction comprising at least one electrode and a temperature sensor. A miniature RF-delivery apparatus is needed to reach a liver and optionally into the liver for therapeutic treatment, the apparatus preferably having temperature sensing means for sensing/controlling the RF energy delivery and force measuring means for sensing/controlling apparatus advancement.
Similarly, a nerve is located within a restricted space which is difficult for a bulky ablation device to access to. A miniature RF-delivery apparatus is needed to reach a nerve for therapeutic treatment, the apparatus preferably having temperature sensing means and force measuring means. In all the above indications, a miniature RF-delivery apparatus should have temperature sensing means for controlling the RF energy delivery according to the appropriate temperature prescribed; and force measuring means for controlling RF energy delivery and for apparatus advancement operations according to the appropriate force prescribed.
One method of reducing the size of cellular tissues in situ has been used in the treatment of many diseases, or as an adjunct to surgical removal procedures. This method applies appropriate heat to the tissues, and causes them to shrink and tighten. It can be performed on a minimal invasive fashion, which is often less traumatic than surgical procedures and may be the only alternative method, wherein other procedures are unsafe or ineffective.
RF therapeutic protocol has been proven to be highly effective when used by electrophysiologists for the treatment of tachycardia; by urologists for treatment of prostates; by neurosurgeons for the treatment of Parkinson's disease; and by neurosurgeons and anesthetists for other RF procedures such as Gasserian ganglionectomy for trigeminal neuralgia and percutaneous cervical cordotomy for intractable pains. Radiofrequency treatment, which exposes a patient to minimal side effects and risks, is generally performed after first locating the tissue sites for treatment. RF energy, when coupled with a temperature control mechanism, can be supplied precisely to the apparatus-to-tissues contact site to obtain the desired temperature for treating a tissue.
A thermocouple is a temperature sensing probe consisting of the junction of two dissimilar metals which has a millivolt output proportional to the difference in temperature between the"hot" junction and the lead wires (cold junction). Temperature sensing using a thermocouple is based on the discovery by Seebeck in 1821 that an electric current flows in a continuous circuit of two different metallic wires if the two junctions are at different temperatures. In electric circuits, the current is dependent on the electromotive force developed and the resistance of the circuit. For accurate temperature measurements, the measuring instrument is constructed so that a no-current electromotive force is measured to eliminate the effects of circuit resistance. The materials used for the wires typically include copper, nickel-chromium, iron, platinum, nickel-aluminum, and Constantan. A good reference book for more information on thermocouples is Perry's Chemical Engineer's Handbook 6.sup.th Edition, published by McGraw-Hill Book Company, 1973.
A thermistor is a temperature-sensing probe manufactured of a mixture of metal oxides. A large change in resistance is exhibited proportional to a change in temperature. Electrical conductors experience a change in resistance with temperature which can be measured with a Wheat-stone-bridge circuit. The relationship for platinum is very exact and hence serves as a primary standard over a wide temperature range. A good reference book for more information on thermistors is Mark's Standard Handbook for Mechanical Engineers 8.sup.th Edition, published by McGraw-Hill Book Company, 1978.
Thermostatic bimetal thermometers can be defined as a composite material made up of strips of two or more metals fastened together. Types of elements used in bimetal thermometers are flat spiral, single helix, and multiple helix. This composite, because of the different expansion rates of its components, tends to change curvature when subjected to a change in temperature. The distal portion of a bimetal thermometer can be straightened to function as an electrode for RF energy delivery to a tissue.
One major drawback of the current RF ablation devices is its bulkiness. In addition to its bulkiness, the force for pushing a conventional catheter into a confined space is not monitored and controlled. A patient is in great risk of injury when the force is undesirably higher than an accepted value. A force measuring means on a RF catheter would request a physician to take appropriate actions when he receives a warning. An existing RF ablation catheter generally comprises at least one electrode and its associated temperature sensing probes. The total space needed for an electrode and its additional temperature probe makes said device not suitable for certain tissue ablation applications due to its restricted location or space. Therefore, there is a clinical need for an improved ablation apparatus system having capabilities of measuring a contact force, measuring a tissue temperature, delivering RF therapeutic energy, and/or controlling the energy delivered for optimal effectiveness in tissue treatment.